Add a gitea skill; point AGENTS.md at it

Forge usage was spread across AGENTS.md, docs/agents/issue-tracker.md, and
whatever the agent remembered about `gh`. Move the how-to-run-`tea` half into a
model-invoked skill so it loads on any issue/PR task, and leave AGENTS.md a
single line of identity plus pointers.

The skill carries only what `tea --help` cannot answer: `gh` is absent so the
harness's `issue://`/`pr://` URIs error out, issues and PRs share one index
space, rendered-box output needs `-o json`, `close` takes no `--comment`,
labels never auto-create, bodies need a heredoc, and a read without
`--comments` silently drops every comment (issue #123: 40 lines bare, 132 with
the flag). Tracker conventions and triage label strings stay in
docs/agents/, cited rather than copied.

CONTEXT.md

@@ -43,13 +43,6 @@ Readers: Progress, Favourite, Lifecycle bucket. Facts about the Series itself be
 to the Series, not here.
 _Avoid_: entry, item, record, subscription
 
-**Orphan Series**:
-A Series no Reader bookmarks. Removing a Bookmark never removes the Series, so the row
-outlives every relationship to it: nothing reads it, no Poll visits it, and it still owns
-a Cover. A state of the Series, not a Lifecycle bucket — it says how many Readers hold it,
-never anything about a Reader.
-_Avoid_: dangling, unused, dead series, stale
-
 **Library**:
 One of the two halves of the collection — manga or novel — selected by a Bookmark's
 `kind`. The web UI and the userscripts each address exactly one Library at a time.
@@ -83,33 +76,6 @@ asked. Every Site has exactly one and no Lane can slow, block or borrow from ano
 a Reader never has one and never influences one.
 _Avoid_: worker, queue, scheduler, batch, wave
 
-**Lane Pass**:
-One sweep of a Poll Lane over the Series due on its Site: what it found waiting, how many it
-read, and whether it declined to work at all. A fact about the Lane rather than about any
-Series — a pass that read nothing is still a pass, and one that declined carries the reason it
-declined, since a Lane resting and a Lane stuck look identical from a count alone. Its record
-outlives the process that made it: "the poller has done nothing for six hours" is only
-answerable by something written down.
-_Avoid_: run, cycle, tick, batch, poll history
-
-**Forced Poll**:
-A Poll the owner asks for by hand instead of waiting for the Series's turn. It jumps its
-Lane's queue and ignores every waiting rule — the rest between Polls, a Sighting standing
-in for a check, a Series only finished Readers hold — but never overrules a Site that is
-refusing us, the Lane's spacing between fetches, or a Series with no page to fetch. Asked
-for by marking the Series, never by commanding the poller, so it happens on the Lane's
-next pass rather than at the moment of asking.
-It also takes whatever Cover the Site publishes today: asking for one is asking to accept the
-page as it now stands, so it is the only read after Acquisition that can replace a Cover.
-_Avoid_: manual poll, refresh, retry, force refresh
-
-**Paused Lane**:
-A Poll Lane the owner has stopped for a bounded time. It makes no Polls until the pause
-expires, so its Series stay due and unstamped exactly as they do when a Site cannot be
-reached. Every pause carries an expiry — a Lane cannot be stopped indefinitely — and it
-outlives a restart, being a fact about the Site rather than about the running process.
-_Avoid_: disabled, off, stopped, suspended, kill switch (that is the deploy-time switch)
-
 **Sighting**:
 What a Reader's browser happened to see of a Series's Latest Chapter while that Reader
 was on the page. It reports the same fact as a Poll but carries none of its authority:
@@ -122,9 +88,9 @@ _Avoid_: client report, user poll, observation, claim
 The single read of a Series page made the moment the Series first exists, giving it
 both its Latest Chapter and its Cover without waiting for the Lane's pace. Distinct
 from a Poll in the two ways that matter: a Reader is present — it is triggered by
-their first Bookmark of that Series — and it establishes a Cover rather than refreshing
-facts, which no Poll does unless the owner forces one. It happens once in a Series's
-life; every later read of the same page is a Poll.
+their first Bookmark of that Series — and it is the only read that establishes a
+Cover rather than refreshing facts. It happens once in a Series's life; every later
+read of the same page is a Poll.
 _Avoid_: initial poll, first fetch, prefetch, warm-up
 
 **New Chapter**: